Signaling system



Oct. 26, 1943. s K AL 2,332,494

SIGNALING-SYSTEM Filed April 23, 1942 AMPL/F/ER I DEM), NETWORK DIFFERENT/AL DETECTOR smvo I PASS FIL TE]? 1 SIG/VAL DETECTOR S. M BABCOCK lM/E N TOPS A. K. HORTON JR.

By M. A. LOGAN A T TOP/V5 V Patented Oct. 26, 1943 I UNITED STATES PATENT "OFF-ICE SIGNALING SYSTEM Stuart M. Babc'ock, Chathfam, Arthur W. Horton, Jr., South Orange, and Mason A. Logan,

Summit, N. l, assignors 't'o Bell Telephone Laboratories,- lncorporated, New York, N; Y., a

corporation of New York I Application April 23, 1942, Serial No. 440,138 g 7 Claims. (01.179-4) This invention relates to signaling systems and particularly to systems in which-alternating currents Within the voice frequency range are .used to transmit signals. 7 I

Objects of the invention are an increase inthe reliability of signal response and a decrease .in

,tion, one such receiver being shown schematically in the drawing-which forms a part of this specification.

The drawing, which consists of a single figure, shows a'telephone line Ll connected to a signal v receiver SR comprising an amplifier and delay the likelihood of false signal operation in systems i in which signals consisting of current of voice frequency are transmitted over linesused for the transmission of voice currents.

It is known that voice' currents, that is currents generated in telephone transmitter'circuits v and transmitted over the associated linearenot symmetrical in wave form, the amplitude of the negative half cycles of current being greater than the amplitudeof the positive half cycles of current or vice versa depending upon the particular circuit arrangement at the station. Since signaling currents are usually symmetrical in this respect and the signal transmitting means signal operation in response tov voice currents or- 5 other non-symmetrical currents of signaling fre-' quency.

According to a feature of the invention the current in a line over which both voice currents and signal currents are transmitted isconn'ected to-a signal receiver comprising an asymmetrypr dif ferential detectorand a signal detector, the differential detector. being effective toprevent-the closing of the signaling circuit under the control of the signal detector in response to asymmetrinetwork, a differential detector, and a signal detector. i

The line Ll-is a line over which voice currents and'voice frequency signaling currents are transomitted and noise or other interference currents are usually present in some degree. The line Li.

is connected 'to the amplifier and delay network by a'transiormerJD, to the differential detector by a transformer. 39, and to the signaldetector byfa transformer 60, the primary. windings of these transformers. being connected inparallel,

as shown, or in series iiiso desired. If the sigline and the primary windin of transformer fill cal. voice currents. Accordin to a further featween signal currents and speech currents is utilized to prevent signal operation in response'to speech currents. I A clear and complete understanding, of :the invention will be facilitated 'by considering a'.signal receiver embodying the features of the invenpolarized relay 21-.

as shown in the drawing or one of the windings of thetransformer 60 may be included in a tuned tube lil.v The amplifierv consists of two. vacuum tubes H .and [2 connected as amplifiers in'push-pull re-.

lationshinretard coils l3 and I4, condensers l5 and I6 and the primary winding of transformer H. The delay network comprises relays I9, 28

and 21 which are controlled by the output of the amplifier for enabling theoperation of the signal relay, 62 if and when signaling current is transmitted over line Ll for a predetermined interval of timafor instance .020 second. The secondary winding of transformer I1 is connected through the full-wave rectifier 18 to the upper operating'windlngof relay [9. Relay i9 is a polarized relay, the left contact of which is normally closed due to theenergization of its-lower biasing winding. "When the current inprimary winding of transformer 11 builds up to a highenough value,

the potential induced in the secondary winding causes the operative energization of-the upper -winding of rela-y lll, whereupon relay l9 opens its left contact, thereby opening a normally closed circuit through the upper, operating winding of The en'ergizaticn of the upper winding of relay 21- is maintained for a short interval of time while condenser Ed is charging, fter which theenergization of the lower biasing ',winding of relay 21-becomes effective to close the right contact of this relay to connect condenser 62, The current charging condenser 26 maintains the operative energization of the upper winding of relay 2! for about .040 second, after which the lower biasing winding of relay 2i] restores the contact springs to normal, thereby disconnecting ground potential from conductor 25. If relay I9 is being held operated by current in line Ll, the release of relay 2B is ineffective to cause the reoperation of relay 21; but, as soon as both of relays l9 and 20 have released, the upper winding of relay 2'! is again energized and relay 2! closes its left contact to discharge condenser 26. Thus, about .020 second after the start of a current in line Ll, ground is connected to conductor 29; and, at the end of an interval of .040 second, ground is disconnected from conductor 29, the continued operation of relay is being ineffective to again connect ground potential to conductor 29.

The differential detector comprises linear amplifier tub-es 3| and 32, transformer 35, linear amplifier tubes 4! and 42, transformer 65, and amplifier detector tubes 5! and 52 so connected that the negative and positive half cycles of the voltage induced in the secondary winding of transformer 38 are amplified and applied through transformer 45 to the grids of self-biasing detector tubes 5| and 52. The voltages applied through transformer 45 cause rectified currents in the grid-cathode circuits of tubes 5| and 52, thereby effecting the charging of condensers 41 and 48; so that the bias of both of these tubes is increased until the effective grid voltage is almost equal to the peak voltage of the applied signal. If the current in line LI is asymmetric in wave form, the final, small current which maintains the charge in condensers 41 and 48, results from the highest positive peak voltage; and the grid of that one of tubes 5! and 52, to which this peak voltage is applied, is less negative than the grid of the other of these tubes. Therefore,

the current in the anode-cathode circuit of the detector tube to which the peak positive voltage is applied will be larger than the current in the anode-cathode circuit of the other of these detector tubes. A portion of the self-biasing voltage developed by detector tubes 5| and 52 is included in the bias of the variable mu amplifier tubes 3! and 32 as an automatic sensitivity control; so that the linear amplifier tubes will not be overloaded by-loud speech or tones. Each of relays 5'! and 58 is a polarized relay having a normally energized biasing winding for holding the contacts in the position shown in the drawing. The current in the output circuit of tube 5| energizes the middle winding of relay 5? and upper winding of relay 53 in series; and the current in the output circuit of tube 52 energizes the middle winding of relay 58 and lower winding of relay 57. The upper and middle windings of relay 58 and the middle and lower windings of relay 5'! are connected so as to be differentially energized; so that,'as long as the current in line Ll is symmetrical, neither of relays 51 and 58 is operated. And in this case the connection of ground potential to conductor 29 by the operation of relay 28, as above described, closes the anode-cathode circuit of tube Bl; so that ourrent of signaling frequency of a high enough energy level to overcome the normal negative bias in the grid-cathode circuit effects the operation of signal relay 62. Relay 62 in turn controls circuits through conductors 83 and E4 to perform any desired signaling operation.

If, however, the negative half cycles of current in line Ll are of higher amplitude than the positive half cycles or the positive half cycles are of higher amplitude than the negative half cycles, the output of tubes 5! and 52 will be sufficiently unbalanced to effect the operation of the one or the other of relays 51 and 58. The condenser 53 is to by-pass the alternating current components of the detected signal and to permit only the direct current components to pass through the differential windings of relays 51 and 58. The operation of either one of relays 5'! and 58 opens the normal connection between conductors 29 and 59 to prevent the closing of the anode-cathode circuit of tube 6! of the signal detector and thereby prevent the operation of signal relay 62.

What is claimed is:

1. In a signaling system in which signals are transmitted by alternating current of symmetrical wave form within the voice frequency range, a signal receiver comprising an input circuit, a signal detector connected to said input circuit, a signal device connected for operation by current in the output circuit of said detector, an asymmetry detector for detecting asymmetry in the wave form of the current in said input circuit, and means controlled by said asymmetry detector for preventing the operation of said signal device in response to voice currents or other currents which are asymmetric in wave form.

2. In a signaling system comprising a line over which voice currents and signaling currents of one or more frequencies within the voice range are transmitted, the signaling currents being symmetrical in wave form, a signal receiver connected to said line, said receiver comprising an input circuit, a signal device, means including a detector operatively connecting said device to said input circuit, an asymmetry detector connected to said input circuit for detecting whether the current therein is of asymmetric wave form, and means rendered effective by said asymmetry detector in response to current of asymmetric wave form in said input circuit for preventing the operation of said signal device.

3. In a signaling system in which signals are transmitted by alternating currents within the voice frequency range, said signaling current being symmetrical in wave form, a signal receiver comprisingan input circuit, a signal detector connected to said input circuit, a signal device connected to the output circuit of said detector, an asymmetry detector connected to said input circuit, means controlled by said asymmetry detector responsive to voice currents or other current of asymmetric wave form in said input circuit for preventing the operation of said signal detector, and means comprising a delay network connected to said input circuit for rendering said signal detector inoperative until the current in said input circuit has continued for a predetermined interval of time.

4. In a signalling system in which signals are transmitted by alternating current within the voice frequency range, said signaling current being symmetrical in wave form, a signal receiver comprising an input circuit, a signal device, means comprising a normally inoperative signal detector connecting said device to said input circuit for operation in response to signaling current, an asymmetry detector connected to said input circuit, means comprisinga delay network responsive to current in said input circuit for rendering said signal detector operative when the current in said input circuit has continued for a predetermined interval of time, and means rendered effective by the operation of said asymmetry detector in case the current in said input circuit is asymmetrical in waveform for preventing the operation of said signal detector.

5. In a signaling system in which signals are transmitted by alternating current of a particular frequency characteristic within the voice frequency range, the signaling current being symmetrical in wave form, a signal receiver comprising an input circuit, a signal detector, a bandpass filter tuned to transmit current of said particular frequency characteristic connecting said signal detector to said input circuit, a signal device connected for operation by current in the output circuit of said signal detector, an asymmetry detector for detecting asymmetry in the wave form of the current in said input circuit and means controlled by said asymmetry detector for preventing the operation of said signal device in response to voice currents or other currents of said particular frequency characteristic which are U asymmetric in Wave form.

6. In a signaling system in which signals are transmitted by alternating current of a particular frequency characteristic within the voice frequency range, said signaling current being symmetrical in Wave form, a signal receiver comprising an input circuit, a signal detector, a bandpass filter tuned. to said particular frequency characteristic connecting said signal detector to said input circuit, a signal device connected to the output circuit of said detector, an asymmetry detector connected to said input circuit, means controlled by said asymmetry detector responsive to voice currents or other current of asymmetric Wave form in said input circuit for preventing the operation of said signal detector, and means comprising a delay network connected to said input circuit for rendering said signal detector inoperative until the current in said input circuit has continued for a predetermined interval of time.

7. In a signaling system in which signals are transmitted by alternating current of a particular frequency characteristic within the voice'frequency range, said signaling current being symmetrical in Wave form, a signal receiver comprising an input circuit, a signal device, means comprising a normally inoperative signal detector for operating said device in response to signaling current, a band-pass filter connecting said signal detector to said input circuit, said filter tuned to pass current of said particular frequency characteristic, an asymmetry detector connected to said input circuit, means comprising a delay network responsive to current in said input circuit for rendering said signal detector operative when the current in said input circuit has continued for a predetermined interval of time, and means rendered effective by the operation of said asymmetry detector in response tocurrent of asymmetrical wave form in said input circuit for prev venting the operation of said signal detector.

STUART M. BABCOCK. ARTHURW. HORTON, J R. MASON A. LOGAN. 

